JP7091461B2 - Positive electrode material for rechargeable lithium-ion batteries - Google Patents

Description

The present invention relates to a lithium transition metal oxide compound that can be applied as a positive electrode material for a rechargeable lithium ion battery. More specifically, the material comprises a mixture of large spherical polycrystalline lithium transition metal oxide compounds and small single crystal lithium transition metal oxide compounds. The positive electrode material enhances battery performance, for example, energy density with high volume density and cycle stability with high compressive strength.

Environmental pollution is a global threat resulting from advanced industrialization, and the world is facing critical situations such as ozone depletion and the greenhouse effect. As environmental regulations are tightened worldwide, electric vehicles (EVs) are attracting attention as an alternative to using green energy as a resource for transportation. Vehicles that are rechargeable and have energy sources with high energy densities that can replace vehicles that use fossil fuels are essential. Lithium-ion batteries (LIBs) are the most promising candidates for such energy sources.

LiCoO ₂ (LCO) has been used as a positive electrode material in most LIBs, for example for portable applications. The main reason is that very high electrode densities are easily achieved. In addition to this advantage, low expansion, high capacity, as well as acceptable safety and cycle life, especially when the charging voltage is increased. Portable batteries are so small that they can tolerate the high cost of Co. Even if the price of cobalt metal is 100 $ / kg, the cobalt cost of a 4Ah smartphone battery is about 2.50 $ or less, which is a small cost compared to the price of a smartphone. This situation is different from that for automotive applications, where the cost of metal in the battery would significantly contribute to the total cost when using LiCoO2.

Therefore, cobalt resources are limited, and according to the Cobalt Development Institute, LCO is a large battery because about 30% of the world's cobalt production is already used in rechargeable batteries. Is not sustainable. Therefore, the lithium nickel-cobalt manganese oxide (hereinafter referred to as "NMC") has an approximate stoichiometry of _LiM'O2 (in the formula, M' ₌ Nix Mn _y Coz), and the resource status is not so high. Since it is not dangerous, it is a promising positive electrode material. NMC has a low cobalt content because cobalt is replaced by nickel and manganese. Nickel and manganese are cheaper than cobalt and relatively abundant, so NMC may replace LCO in large batteries.

An ideal positive electrode material for EV is required to have a high weight energy density (Wh / g) at a relatively low voltage and to provide a high electrode density. The former means that a positive electrode material with a higher Ni content is more desirable, while the latter means that a higher press density is required. Theoretically, as the amount of Ni in the NMC increases, the capacity of the positive electrode material increases, and a higher weight energy density can be obtained. However, the higher the Ni content of the positive electrode material, the more brittle it becomes. Therefore, attempts to achieve high electrode densities using high Ni cathode materials (ie, those with a Ni content of 60 mol% or more of the transition metal content) are more difficult than those with low Ni materials. It will be a thing. This attempt requires new concepts in material design other than those currently used in batteries.

The volumetric energy density of the positive electrode material can be calculated by multiplying the weight energy density (Wh / g) and the electrode density (g / cm ³ ). The higher the electrode density, the more powder can be filled into a given volume and thus the available energy can be increased. Since the electrode density correlates well with the press powder density of the positive electrode material, a material having a high press powder density is desired.

During the preparation of the positive electrode, a roll press process (referred to as an electrode calendar processing process) is applied to form the components of the electrode containing the positive electrode material. Although the positive electrode material particles may have a tendency to be broken, powders that can be formed more easily and particles with lower brittleness have a lower frequency of breakage. Particle destruction can have serious consequences. The destroyed positive electrode material not only becomes denser as the pores collapse, but also the surface area increases. In this molded electrode region, the electrolytic solution that limits the rapid diffusion of lithium ions in the electrolyte is depleted, resulting in poor rate performance. An increase in surface area is not desirable as it increases the total area and may cause unwanted side reactions between the electrolyte and the positive electrode material. Therefore, the ideal positive electrode material has particles that are not brittle.

Generally, the positive electrode powder is coated on both sides of the base film and the aluminum foil that acts as a current collector. Basically, if the pressure applied during the calendaring process is high enough, any positive electrode material can be pressed until the electrode density is high enough. However, if the pressure is too high, it will damage the electrodes. In particular, the aluminum foil will be damaged, stretched and "wavy". At the same time, the positive electrode material particles are press-fitted into the aluminum foil. We call this the "electrode bite" effect. The aluminum foil can be torn or broken at such electrode bite points during further processing. A suitable positive electrode material is required to be capable of forming into a high-density electrode even at a low pressure without causing electrode biting.

Furthermore, the particle size distribution of the positive electrode material is important. Larger particles tend to have better press densities. However, they also cause more electrode bites. The worst scenario occurs when the positive electrode material has very few large particles. When the larger particles are located on top of the smaller particles, the smaller particles easily penetrate deep into the aluminum foil and function as a knife. This effect can be minimized by limiting the maximum size of the particle size distribution (D99 or D100).

An object of the present invention is a novel positive electrode having a high energy density based on a higher press density without causing both particle breakage and electrode bite problems during the electrode manufacturing process, as well as particle breakage problems during the cycle in the battery. To provide the material.

In the present invention, the particle size distribution (% by volume vs. size) is evaluated by laser diffraction, which quantifies the percentage of the relative volume of the particles by the size of the particles. The values of D10, D50, D90, D99, and D100 are defined as particle sizes at 10%, 50%, 90%, 99%, and 100% of the cumulative particle size distribution relative to volume. The span of the particle size distribution is defined as (D90-D10) / D50 and is used as an indicator of the width of the particle size variation.

From the first aspect, the present invention is a bimodal lithium transition metal oxide powder mixture for a rechargeable battery.
A first lithium transition metal oxide powder comprising a material A having a layered crystal structure consisting of the element Li, a transition metal composition M, and oxygen and having a particle size distribution having a span of less than 1.0.
Monolithic form and general formula Li _{1 + b} N'1 _-b O ₂ [In the formula, -0.03 ≤ _b ≤ 0.10 and N'= Ni _x M " _y Coz _Ed , 0.30 ≤ x ≤0.92, 0.05≤y≤0.40, 0.05≤z≤0.40, and 0≤d≤0.10, where "M" is either one or both of Mn and Al. E is a dopant different from M'], including a second lithium transition metal oxide powder, the first powder having an average particle size D50 of 10-40 μm. , The second powder has an average particle size D50 of 2-4 μm, and the weight ratio of the second powder in the bimodal mixture is 15-60% by weight, the bimodal lithium transition metal oxide. A system powder mixture can be provided. The particles of the second powder can get stuck in the interparticle voids of the first powder.

In different embodiments, it has the following characteristics:
The material A is the general formula Li _{1 + a} Co _{1-m M'm} O ₂ [in the formula, -0.05 ≦ a ≦ 0.05 and 0 ≦ m ≦ 0.05, and M'is Al, Ca, Si. , Any one or more of the metals in the group consisting of Ga, B, Ti, Mg, W, Zr, Cr, and V], and in certain embodiments, a bimodal mixture. A bimodal powder mixture in which the weight ratio of the second powder in the mixture is 15 to 25% by weight.
Material A is polycrystalline and has the general formula Li _{1 +} a'M _1- a'O ₂ [in the formula, -0.03 ≤ a'≤ 0.10 and M = Ni _{x'Mn y'Coz ' Ed. '} 0.30 ≤ x'≤ 0.92, 0 ≤ y'≤ 0.40, 0.05 ≤ z'≤ 0.40, 0 ≤ d'≤ 0.05, and x'+ y'+ z '+ D'= 1 and E'is any one of the elements in the group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, V, S, F, or N. A bimodal powder mixture having particles having more than one (one of more), and in certain embodiments, the weight ratio of the second powder in the bimodal mixture is 20-60% by weight. ..
The powder mixture mentioned immediately before this may be composed of particles having a surface layer containing a homogeneous mixture of elements of M, LiF, and Al ₂ O ₃ .
In the powder mixture mentioned just before this, the first powder may have an average particle size D50 of 10-25 μm and a span of 0.8 or less or even 0.7 or less.
0.60 ≤ x'≤ 0.92, 0 ≤ y'≤ 0.30, 0.10 ≤ z'≤ 0.30, and in a particular embodiment, d'= 0, as described above. Bimodal powder mixture in morphology.
E is any one or more of the elements in the group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, V, S, F, or N (one of more). , Bimodal powder mixture.
Both the first powder and the second powder have an aspect ratio around 1 (or substantially equal to 1), preferably equal to 1.0 ± 0.1, more preferably equal to 1.00 ± 0.01. Bimodal powder mixture with ratio. In the framework of the present invention, the aspect ratio of a particle is determined based on the evaluation of the particle circumference U, the particle surface A, and the diameter derived from each size. The above diameter is obtained from the following equation.
d _U = U / π d _A = (4A / π) ^1/2

The aspect ratio (f) of the particle is derived from the particle circumference U and the particle surface A according to the following equation.

式中、（ＰＤＭ後のＤ１０）及び（ＰＤＭ前のＤ１０）は、それぞれ、２００ＭＰａの圧力の適用後及び適用前のＤ１０値である、二峰性粉末混合物。
３．０ｇ／ｃｍ^３以上又は更には３．２超及び場合によっては更には３．３ｇ／ｃｍ^３以上の第２の補正されたプレス密度を有し、第２の補正されたプレス密度が式ＰＤ／１００ｘ（１００－ＩＢ）で計算され、式中、ＰＤは、２００ＭＰａの圧力下でのプレス密度であり、ＩＢは、以下のように計算された二峰性粉末の比表面積ＢＥＴの増加であり、

式中、（ＰＤＭ後のＢＥＴ）及び（ＰＤＭ前のＢＥＴ）は、それぞれ、２００ＭＰａの圧力の適用後及び適用前のＢＥＴ値である、二峰性粉末混合物。 For ideal spherical particles, the sizes of d _A and d _U are equal and the resulting aspect ratio is 1. The aspect ratio can generally be determined using, for example, an SEM image of the material.
With a first corrected press density of 3.2 g / cm ³ or more or even 3.3 g / cm ³ or more, the first corrected press density is calculated by the formula PD / 100x (100 + ID10). In the formula, PD is the press density under a pressure of 200 MPa, and ID10 is the increase in the D10 value in the particle size distribution of the bimodal powder calculated as follows.

In the formula, (D10 after PDM) and (D10 before PDM) are bimodal powder mixtures having D10 values after and before application of a pressure of 200 MPa, respectively.
It has a second corrected press density of 3.0 g / cm ³ or more or even more than 3.2 and in some cases even 3.3 g / cm ³ or more, and the second corrected press density is the formula. Calculated at PD / 100x (100-IB), in the formula PD is the press density under a pressure of 200 MPa and IB is the increase in the specific surface area BET of the bimodal powder calculated as follows: can be,

In the formula, (BET after PDM) and (BET before PDM) are bimodal powder mixtures having BET values after and before application of a pressure of 200 MPa, respectively.

From the second aspect, the present invention comprises the bimodal powder mixture according to any one of the above-described embodiments, a binder, and a conductive agent, and the bimodal powder mixture in the positive electrode mixture. The positive electrode mixture is at least 90% by weight, and the positive electrode mixture can provide a positive electrode mixture for rechargeable batteries having a density of at least 3.65 g / cm ³ when pressed under 1765.2 N.

式中、（ＰＤＭ後のＤ１０）及び（ＰＤＭ前のＤ１０）は、それぞれ、２００ＭＰａの圧力の適用後及び適用前のＤ１０値である、実施形態１～７のいずれか１つに記載の二峰性粉末混合物。
９．二峰性粉末が、３．０ｇ／ｃｍ^３以上の第２の補正されたプレス密度を有し、第２の補正されたプレス密度が式ＰＤ／１００ｘ（１００－ＩＢ）で計算され、
式中、ＰＤは、２００ＭＰａの圧力下でのプレス密度であり、ＩＢは、以下のように計算された二峰性粉末の比表面積ＢＥＴの増加であり、

式中、（ＰＤＭ後のＢＥＴ）及び（ＰＤＭ前のＢＥＴ）は、それぞれ、２００ＭＰａの圧力の適用後及び適用前のＢＥＴ値である、実施形態１～８のいずれか１つに記載の二峰性粉末混合物。
１０．粉末混合物の粒子が、Ｍ、ＬｉＦ、及びＡｌ_２Ｏ_３の元素の均質混合物を含む表面層を有する、実施形態３又は４に記載の二峰性粉末混合物。
１１．充電式電池用の正極混合物であって、実施形態１～１０のいずれか１つに記載の二峰性粉末混合物と、バインダーと、導電剤と、を含み、正極混合物中の二峰性粉末混合物の重量比は、少なくとも９０重量％であり、正極混合物は、１７６５．２Ｎ下でプレスされたときに少なくとも３．６５ｇ／ｃｍ^３の密度を有する、充電式電池用の正極混合物。 The present invention also relates to the following embodiments 1 to 11.
1. 1. A bimodal lithium transition metal oxide powder mixture for rechargeable batteries.
It contains particles of material A having a layered crystal structure consisting of element Li, transition metal composition M, and oxygen, and has a particle size distribution characterized in that (D90-D10) / D50 is less than 1.0. , The first lithium transition metal oxide powder and
The material B containing the single crystal particles is contained, and the particles include the general formula Li _{1 + b} N'1 _-b O ₂ [in the formula, -0.03 ≤ b ≤ 0.10, and N'= Ni _x M " _y Co. _z Ed, 0.30 ≦ x ≦ 0.92, 0.05 ≦ y ≦ 0.40, 0.05 ≦ z ≦ 0.40, and 0 ≦ _d ≦ 0.10. The first powder comprises a second lithium transition metal oxide-based powder, which is either one or both of Mn and Al, where E is a different dopant than M'. The second powder has an average particle size D50 of 10-40 μm, the second powder has an average particle size D50 of 2-4 μm, and the weight ratio of the second powder in the bimodal mixture is 15-60% by weight. A bimodal lithium transition metal oxide powder mixture.
2. 2. The particles of the material A are the general formula Li _{1 + a} Co _{1-m M'm} O ₂ [in the formula, -0.05 ≤ a ≤ 0.05 and 0 ≤ m ≤ 0.05, and the material A is 20 μm or more. M'has one or more of the metals in the group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, and V]. The bimodal powder mixture according to the first embodiment, wherein the weight ratio of the second powder in the bimodal mixture is 15 to 25% by weight.
3. 3. Material A is polycrystalline and has the general formula Li _{1 +} a'M _1- a'O ₂ [in the formula, -0.03 ≤ a'≤ 0.10 and M = Ni _{x'Mn y'Coz ' Ed. '} 0.30 ≤ x'≤ 0.92, 0 ≤ y'≤ 0.40, 0.05 ≤ z'≤ 0.40, 0 ≤ d'≤ 0.05, and x'+ y'+ z '+ D'= 1 and E'is any one of the elements in the group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, V, S, F, or N. The bimodal property according to embodiment 1 or 2, wherein the particles have one or more particles, and the weight ratio of the second powder in the bimodal mixture is 20 to 60% by weight. Powder mixture.
4.0.60 ≤ x'≤ 0.92, 0 ≤ y'≤ 0.30, 0.10 ≤ z'≤ 0.3. The bimodal powder mixture according to the third embodiment.
5. E is any one or more of the elements in the group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, V, S, F, or N (one of more). , The bimodal powder mixture according to any one of embodiments 1 to 4.
6. The first powder has an average particle size of 10 to 25 μm and a particle size distribution of 0.8 or less (D90-D10) / D50, according to any one of claims 3 to 5. Bimodal powder mixture.
7. The bimodal powder mixture according to any one of embodiments 1 to 6, wherein both the first powder and the second powder have an aspect ratio substantially equal to 1.
8. The bimodal powder has a first corrected press density of 3.2 g / cm ³ or more, and the first corrected press density is calculated by the formula PD / 100x (100 + ID10), in the formula PD. Is the press density under a pressure of 200 MPa, and ID10 is an increase in the D10 value in the particle size distribution of the bimodal powder calculated as follows.

In the formula, (D10 after PDM) and (D10 before PDM) are D10 values after and before application of a pressure of 200 MPa, respectively, which are the two peaks according to any one of embodiments 1 to 7. Sex powder mixture.
9. The bimodal powder has a second corrected press density of 3.0 g / cm ³ or greater, and the second corrected press density is calculated by the formula PD / 100x (100-IB).
In the formula, PD is the press density under a pressure of 200 MPa, and IB is the increase in the specific surface area BET of the bimodal powder calculated as follows.

In the formula, (BET after PDM) and (BET before PDM) are BET values after and before application of a pressure of 200 MPa, respectively, according to any one of embodiments 1 to 8. Sex powder mixture.
10. The bimodal powder mixture according to embodiment 3 or 4, wherein the particles of the powder mixture have a surface layer containing a homogeneous mixture of elements of M, LiF, and Al ₂ O ₃ .
11. A bimodal powder mixture for a rechargeable battery, comprising the bimodal powder mixture according to any one of embodiments 1 to 10, a binder, and a conductive agent, and the bimodal powder mixture in the positive electrode mixture. The positive weight mixture is at least 90% by weight and the positive electrode mixture has a density of at least 3.65 g / cm ³ when pressed under 1765.2 N.

It is an FE-SEM image (magnification x1000) of EX-A-01. It is an FE-SEM image (magnification x10000) of EX-B-02. PD as a function of ID10 (x-axis (unit%)) of Example 1 (y-axis (unit g / cm ³ )) PD as a function of D50 (x-axis (unit: μm)) of compound B of Example 2 (y-axis (unit: g / cm ³ )) IB as a function of the proportion of compound B in Example 2 (x-axis (unit%)) (y-axis (unit%)) R. of Example 3 E. B. ED as a function of (x-axis (unit%)) (y-axis (unit g / cm ³ )) It is a cross-sectional FE-SEM image (magnification x1000) of CEX3-02. It is a cross-sectional FE-SEM image (magnification x1000) of EX3. Relative capacitance as a function of the number of full cell cycles of Example 4, where the full cell cycle condition is 4.35V-3.00V at 45 ° C. (y-axis (unit%)). Relative capacitance as a function of the number of full cell cycles of Example 5, where the full cell cycle condition is 4.45V-3.00V at 25 ° C. (y-axis (unit%)).

The particles of the conventional NMC positive electrode material are usually spherical and always polycrystalline. In order to increase the volume density, the present invention can be used as a positive electrode material for lithium-ion batteries, large ordinary spherical polycrystalline compounds (also referred to as compound A) and small monolithic filler compounds (also referred to as compound A). Further also referred to as compound B), a lithium transition metal oxide "bimodal PSD" compound (also referred to as compound C) containing such compounds A and B having a specific weight ratio. offer. Since the particles of compound A are spherical, there are voids between the particles. Theoretically, in an equivalent closed packing system, the maximum volume fraction of the space occupied by the spherical particles is about 74%. The remaining 26% are voids that can be filled with smaller particles. Therefore, the volume density can be increased by using smaller particles (Compound B) in an appropriate amount. In practice, the void volume depends on the morphology of the matrix formed by compound A. Compound B needs to be well fitted in the voids to maximize volume density. Since the fine particle fraction can have a very high specific surface area, it may be excessively involved in unwanted side reactions that may occur with the electrolyte, shortening battery cycle life. Since the fine particles of the present invention have a smaller surface area, they are more resistant to these side reactions. The positive electrode material having the bimodal particle size distribution of the present invention also provides a high press density, and the positive electrode material (Compound C) has a high energy density, and the particles are broken (or cracked) and the electrode is bitten. There are few problems in electrode processing such as.

The particle size distribution of compound C affects the fluidity and molding properties of the compound, and both the fluidity of the powder and the moldability of the powder are important for achieving high electrode density in electrode preparation. Larger particles typically flow more easily than smaller ones, and more spherical particles flow more easily than those with a higher aspect ratio. A typical industrial process for preparing a lithium transition metal composite oxide, which includes a co-precipitation step, a screening step, a filtration step, a milling step, and a cyclone separation step, is whether the particle shape is more spherical (aspect ratio of 1). Whether it is close to) is determined. However, the powder particle size usually varies from lot to lot. The natural particle size distribution of this type of material typically has a span of 1.20 to 1.50. In this context, narrow span refers to a span smaller than 1. In practice, LIBs used in EVs typically require a specific D50 range of positive electrode material in the 3 μm to 25 μm range to obtain the best electrochemical performance. In a positive electrode material having a general span, when D50 is large, large particles (such as particles having a volume corresponding to D99 or D100) exceed or are close to the thickness of the positive electrode (usually thinner than 50 μm). When the pressure during calendar processing is transmitted to the smaller particles through the largest particles, a large force is locally generated on the ductile aluminum foil, resulting in particle breakage, electrode biting, and after calendar processing. It means that there is a risk of electrode separation. Applying a positive electrode material with a narrow span (compound A is applicable in the present invention) is greater than the D50 and corresponding, especially when increasing the pressure during electrode calendar processing to reach higher electrode densities. It will be possible to use powders with smaller D100, D99, or D99 / D50.

There are several promising preparation routes for obtaining compound A with a narrow span. In a preferred embodiment, compound A is prepared from a mixed transition metal precursor (hereinafter referred to as A1). In practice, compound A has a particle size distribution and morphology similar to that of precursor A1. Therefore, A1 also has a narrow particle size distribution. A1 can be a mixed metal hydroxide, a mixed metal oxyhydroxide, a mixed metal oxide, a mixed metal carbonate, or a mixture thereof. A1 is generally prepared by a precipitation process. For example, a flow of a dissolved metal salt such as MSO ₄ (M = Ni, Co, Mn) and a dissolved base such as NaOH is supplied to the reactor with stirring. In addition, an additive flow such as ammonia can be added to the reactor. The mixed transition metal hydroxide (MTH) product precipitates, is filtered and dried. For example, by applying suitable process control, as disclosed in US Pat. No. 9,028,710, the precipitation process yields a narrow span precursor A1. (A) Batch precipitation, repeated batch precipitation, or precipitation during continuous removal of the original slurry, (b) a cascade of reactors, i.e., the product of one reactor is fed to the next reactor. Narrower by several methods, including several reactors connected in series, (c) continuous precipitation with classification and back-feeding of particles, or (d) normal continuous precipitation. You can get a span. In the case of normal continuous precipitation, the form of the mixed hydroxide generally does not have a narrow span. However, the desired form is obtained by a separate classification step. The classification can be a wet process (eg, using hydrocyclone, draft tube, etc.) or a dry process (eg, air classification). The classification can be performed before the lithium conversion step or after the lithium conversion step. In the lithium conversion step, A1 is blended with a lithium source, and then one or more firing steps are performed to carry out a lithium transition metal oxide (hereinafter, A2). (Called) is prepared. Finally, compound A is prepared by suitable post-treatment of A2 such as milling, classification, or sieving.

Compound A having a narrow span is preferable for the above reasons, but it is not effective to use only compound A having a narrow span in order to achieve a high electrode density. The powder molding density is simply limited by voids between multiple particles of similar size. Particle fracture under excessive calendar processing can improve the electrode density to some extent. However, particle destruction is not preferred for other reasons (above) such as cycle stability during the cycle and side reactions. Therefore, the use of compound A with smaller filler materials is also preferred to achieve high electrode densities.

As mentioned above, small particles have a large surface area and can cause problems during the preparation of slurries during the electrode coating process and during the cycle by increasing side reactions with the electrolyte. It is a drawback of PSD. In order to minimize the increase in surface area in the product to which the bimodal PSD is applied, the small particles need to have a smooth surface and a low open porosity. Small particles also need to be as hard as possible, as the surface area of the product can increase further during the calendaring process. In addition, to achieve high density, small particles should not have internal porosity. This leads to the use of compound B "monolithic" materials that meet the above requirements. The "monolithic" morphology refers to a morphology in which the secondary particles contain only one type of primary particle. In the literature, they are also referred to as single crystal particle materials, monocrystalline particle materials, and integral particle materials. The preferred shape for the primary particles can be described as a pebble stone shape with an aspect ratio near 1 (or substantially equal to 1). For example, as disclosed in US Pat. No. 9,184,443, monolithic morphology can be achieved by high sintering temperatures, longer sintering times, and the use of greater excess lithium. The monolithic material has a smooth surface and few internal pores, so that the surface area is small and the particle strength is high. However, since the industrial technology is not sufficiently matured, the monolithic positive electrode material cannot be used as a large positive electrode material (Compound A). The manufacturing process for monolithic materials needs to be more optimized, as much higher and longer sintering temperatures are required to obtain "large" monolithic positive electrode materials.

In the present invention, the small monolithic particles (Compound B) can have a particle size distribution of 2 μm ≦ D50 ≦ 4 μm. If the average particle size exceeds 4 μm, the battery performance may deteriorate and the effect as a filler may be lost. Conversely, if the particle size is too small (ie, less than 2 μm), it will be difficult to prepare the powder using current level processes. For example, the powder cannot be easily sieved because the particles aggregate. In addition, it is difficult to obtain a product that is homogeneously mixed with a large positive electrode material due to agglomeration. Regarding the manufacturing process, for example, as disclosed in US Patent Application Publication No. 2017/0288223, a monolithic positive electrode material having a D50 of about 3 μm can be manufactured by a currently known industrial process. Effectively, there are many promising processes for producing monolithic compound B. Basically, the choice of precursor determines the details of the process. A typical process involves blending a transition metal precursor (referred to as B1) with a lithium source, followed by calcination, followed by a carefully designed milling process. B1 can be a mixed metal hydroxide, a mixed metal oxyhydroxide, a mixed metal oxide, a mixed metal carbonate, or a mixture thereof. In this process, the morphology of PSD and compound B is largely determined by calcination and milling conditions and is less dependent on the PSD of the mixed transition metal precursor (B1). In particular, the need to supply B1 powder, which is a specially shaped particle, is low.

Surprisingly, when monolithic compound B is used as a filler, the breakdown of compound A particles with narrow spans can be better suppressed by the buffering effect of the monolithic filler. Compound A is generally brittle because it is polycrystalline, and the higher the Ni content, the more brittle it becomes. However, even when compound A has a high Ni content such as 87 mol% (to total transition metal content), the occurrence of disruption of compound A particles mixed with compound B is very limited. To. Due to the synergistic effect of the components, it is expected that the electrodes will be less damaged even after severe calendar processing. In particular, the electrode density is highest when 20% to 60% monolithic compound B is used with narrow span compound A. Therefore, the products proposed in the present invention are suitable for application to electrodes with high energy density. The small particles are brittle and are "sracticed", that is, the small particles are destroyed during pressing and the space between the large particles is filled, so that the buffer effect causes the large particles to break. The state-of-the-art technique of preventing is different from the approach of the present invention. Surprisingly, the monolithic small particles also prevent the destruction of large particles, even though they are hard. The authors speculate that this property is associated with easy realignment and slippage due to the smooth surface and special gravel shape.

The positive electrode active material (Compound C) containing the compound A having a narrow span and the monolithic compound B can be prepared by various methods. The first simple method is a physical blend of compound A and compound B at the correct fractionation ratio (compound B is 20-60% by weight). Physical blending can be done by any industrial blending device such as a Lodige blender. Any nanoscale additive can be blended together in the physical blend as it is possible to allow surface coating or improve fluidity. Additional heat treatment steps after blending are possible. The second method is to blend A1 (MTH), monolithic compound B, and a lithium source, followed by calcination and post-treatment. Lithium-deficient compound A'(eg, having a molar ratio of Li / M = 0.80) can be used in place of A1. The amount of lithium source can be adjusted according to the final Li / M ratio and A'ratio. The added lithium reacts with A1 or the lithium-deficient compound A during calcination to form compound A. Since this firing temperature is not as high as the firing temperature of the monolithic compound B, this firing step does not affect the properties of the monolithic compound B.

In contrast to NMC, LCO works well even with large particles and single crystal type. Single crystal LCOs show good performance and it is not necessary to utilize polycrystalline compounds. Commercially available LCO materials usually have a "potato" shaped spherical morphology, with secondary particles consisting of one or very few crystallites.

The authors found that the application of a monolithic NMC filler could also have a significant effect on the LCO-based positive electrode material as compound A. In particular, if the LCO particles are large (typically about 20 μm, more preferably about 25 μm, or even 30 μm) and the PSD distribution has a narrow size distribution, mixing monolithic NMCs will further increase the electrode density. Can be increased. The highest press density is reached when the mass fraction of the monolithic NMC is about 15-25%. The mass fraction of monolithic NMCs in LCO-based positive electrode materials reaching 15-25% provides some additional advantages in addition to high density. First, since NMC has a higher capacity than LCO, the specific capacity increases. Second, NMC has a lower basic cost of metal (particularly lower Co content), which can reduce the cost. Third, in special implementations, it may be desirable to add NMC prior to the final heating step, as NMC can adsorb excess lithium from the LCO.

The current level of LCO is charged to a high voltage. 4.35V is standard, 4.4V is available and 4.45V is promising in the future. The authors found that monolithic NMC fillers work very well in mixtures with LCO-based positive electrode materials even at high charging voltages. In particular, good cycle stability is achieved and no further expansion is observed when storing the charged battery at high temperatures.

In conclusion, the invention combines the following aspects:
1) Since the LIB requires a high energy density, it is possible to increase the volumetric energy density by using two or more positive electrode materials having different particle sizes. The choice of different positive electrode material sizes and their weight ratios is a feature of the present invention.
2) Among the components of the positive electrode, the material having the largest particle size determines the maximum particle size of the entire positive electrode material. Since the average particle size of the positive electrode material tends to increase, the volume density of the entire positive electrode generally increases. However, the maximum particle size does not have to be as small as possible for electrode processing purposes.
3) The surface area of the entire positive electrode material is determined by the material having the smallest particle size among the components of the positive electrode. The surface area of the positive electrode material needs to be limited to avoid unwanted side reactions.
4) The particles of the positive electrode material may crack not only during the electrode treatment, that is, the calendar processing process, but also during the cycle. Cracking of the particles creates additional surfaces, resulting in an undesired increase in surface area. Therefore, the positive electrode material needs to be as hard as possible.

Evaluation of powders on real electrodes requires a lot of work, such as slurry preparation, coating and drying. Therefore, these powders are usually investigated, such as by the press powder density method, which is widely applied in the industry. In this method, the powder can be filled into a mold, pressed with a specified force, eg 200 MPa, the thickness of the resulting pellets can be measured and the known mass can be used to calculate the powder density. In general, there is a good correlation between the density of the pressed powder and the density of the electrodes calendared while applying the force equivalent to that used in the above method. This press density method can then be used to predict the electrode density.

Both PSD analysis and surface area analysis (using BET theory) are performed before and after the application of a particular pressure to determine the degree of particle fracture and surface area increase after the calendaring process. For the press density measurement in the present invention, a pressure of 200 MPa is applied. This pressure is moderate and is high enough to break some of the particles if the positive electrode material has normal brittleness. This pressure is also low enough to avoid excessive molding. For example, powders that are not well formed under this pressure cannot achieve high densities. Therefore, by applying a pressure of 200 MPa, it is possible to distinguish between a positive electrode material powder that easily achieves high density and a positive electrode material powder that requires a higher pressure for molding. The latter powder is a powder that causes electrode damage due to "bite". Therefore, the resulting density is a measure of the electrode density that can be achieved without undue damage to the electrodes.

In addition, a pressure of 200 MPa makes it possible to quantify damage to the powder during pressing. If the powder is very brittle and not easily molded, the particles will be destroyed. Similar fractures occur at electrodes during calendar processing. In addition to avoiding damage to the alumina foil, avoiding powder damage achieves good cycle life, as the broken particles increase the surface area and result in fast side reactions. Is important to. In addition, the broken particles may have poor electrical contact. Finally, if the broken particles are small, they can diffuse through the separator into the electrolyte and damage the anode. Fracture during electrode treatment can be estimated from the results of the powder press. When the particles are destroyed, finer particles are produced. Therefore, the PSD changes and additional new surface area is created. Damage during powder pressing can be quantified by (1) analysis of PSD curves before and after pressing, and (2) increase in BET before and after pressing. As the standard PSD curve moved more to the left (caused by the generation of smaller particles) and the BET increased more, more powder damage occurred. A simple approach for quantifying particle destruction by PSD is by using the numerical value of ID10. This numerical value is defined as ID10 = (D10 after PDM-D10 before PDM) / D10 before PDM (represented by%), and PDM is a press density measurement value described below. If the particles are destroyed and finer particles are produced, the value of ID10 is negative. The larger the absolute value of this number, the finer the particles were produced. Or vice versa, if the powder is easily formed without breaking, the cushioning effect prevents breaking and high density is obtained without causing massive particle damage. In this case, the absolute value of ID10 is close to zero. US Pat. No. 8,685,289 describes the same method for assessing particle strength.

A similar approach is possible by quantifying the damage due to increased BET by IB number. This numerical value is defined as IB = (BET after PDM-BET before PDM) / BET (unit%) before PDM. The IB is usually positive, and the smaller the IB, the less likely it is that particle damage will occur.

プレス後、粉末を、「Ｂ）ＢＥＴ分析」及び「Ｃ）ＰＳＤ測定」によって更に調べる。 In the examples, the following analysis method is used.
A) Press density measurement (PDM)
The press density (PD) is measured as follows: 3 g of powder is filled into a pellet die with a diameter "d" of 1.3 cm. A uniaxial pressure of 200 MPa is applied to the pellet for 30 seconds. After relieving the load, the thickness "t" of the pressed pellet is measured. The press density is then calculated as follows.

After pressing, the powder is further examined by "B) BET analysis" and "C) PSD measurement".

ＰＤＭ：２００ＭＰａの圧力下でのプレス密度測定 B) BET analysis A) The specific surface area of the powder before and after PD measurement is analyzed by the Brunar-Emmett-Teller (BET) method using the Micrometrics Tristar 3000. Prior to measurement, the powder sample is heated under nitrogen (N ₂ ) gas at 300 ° C. for 1 hour to remove the adsorbed chemical species. Place the dried powder in a sample tube. The sample is then degassed at 30 ° C. for 10 minutes. The instrument will perform a nitrogen adsorption test at 77K. From the nitrogen isothermal absorption / desorption curve, the total specific surface area of the sample can be obtained in units of m ² / g.
The change in BET specific surface area before and after pressing under 200 MPa is calculated as follows:

PDM: Press density measurement under pressure of 200 MPa

Ｄ１０の増加（又は減少）及びＢＥＴの増加の両方によるプレス密度への効果は、２００ＭＰａの圧力下での粉末の損傷を定量するのに良い基準として使用することができる。本発明の生成物について得られた「補正ＰＤ」は、「ＰＤ×（１００＋ＩＤ１０）÷１００」が３．２ｇ／ｃｍ^３以上の値、「ＰＤ×（１００－ＩＢ）÷１００」が３．０ｇ／ｃｍ^３以上の値を有する。 C) PSD measurement A) Before and after PD measurement, the powder is dispersed in an aqueous medium, and then the particle size distribution (PSD) of the particles is analyzed using a Malvern Mastersizer 3000 equipped with a Hydro MV wet dispersion accessory. .. In order to improve the dispersion of the powder in the aqueous medium, sufficient ultrasonic irradiation and stirring are applied, and an appropriate surfactant is added. The change in D10 before and after pressing under 200 MPa is calculated as follows:

The effect on press density by both increasing (or decreasing) D10 and increasing BET can be used as a good criterion for quantifying powder damage under pressure of 200 MPa. The "corrected PD" obtained for the product of the present invention has a value of 3.2 g / cm ³ or more for "PD x (100 + ID10) ÷ 100" and 3.0 g for "PD x (100-IB) ÷ 100". It has a value of / cm ³ or more.

D) FE-SEM analysis The morphology of the material is analyzed by scanning electron microscopy (SEM). This measurement is performed by a JEOL JSM 7100F scanning electron microscope device at 25 ° C. under a high vacuum environment of ^9.6x10-5 Pa. Image of the sample is recorded at several magnifications (x1,000-10,000) to demonstrate the monolithic structure of the material. To define the monolithic properties, the number of primary particles in the secondary particles is measured on an SEM image (magnification 5000x) of 10 randomly selected secondary particles. Since the SEM image shows only the morphology of the powder from the top surface, the primary particles are counted within the visible range of the SEM image.

E) Electrode density analysis The positive electrode is prepared by the following procedure: positive electrode active material, Super-P (Super-PTM Li commercially available from Timcal), and graphite as a conductive agent (KS-6 commercially available from Timcal). ), And polyvinylidene fluoride (PVdF1710 commercially available from Kureha) as a binder are added to NMP (N-methyl-2-pyrrolidone) as a dispersion medium. The mass ratio of the positive electrode material, Super-P, graphite, and the binder may be set to 95/3/1/2. Then, the mixture is kneaded to prepare a mixed slurry of the positive electrode, and the slurry is coated on both sides of the positive electrode current collector which is a 20 μm thick aluminum foil. The electrodes are then dried. The thickness of the electrode before calendar processing is about 160 μm. Calendar processing is performed by a commercially available roll presser (manufactured by Roh-tech). The roll presser has two metal rolls with a diameter of 25 cm. A dried electrode is passed through a roll presser with the pressure set to 180 Kgf (1765.2 N) and the gap between the two rolls set to 0.
The electrode density can be calculated by the following equation.

F) Quantitative determination of electrode bite Using argon gas as a beam source, the cross section of the electrode prepared by the analysis method E) is processed by an ion beam cross section polisher (CP) device which is JEOL (IB-0920CP). Mount the positive electrode on aluminum foil. Attach the aluminum foil to the sample holder and place it inside the device. The voltage is set to 6.5 kV with a duration of 3.5 hours. The cross section of the positive electrode is analyzed by FE-SEM analysis. Four cross-section FE-SEM images are obtained at a magnification of 1000 times, and the (cross-section) area of the Al foil in the obtained images is analyzed by software called "ImageJ". The relative area of the aluminum foil is used as a reference for quantifying the degree of electrode biting after calendar processing.

H) Coin battery test Regarding the production of the positive electrode, the weight ratio is 90: 5: 5, and the electrochemically active material, conductor (Super P, Timcal), binder (KF # 9305, Kureha) are used as the solvent (NMP, Mitsubishi). ) Is prepared by a high-speed homogenizer. The homogenized slurry is spread on one side of the aluminum foil using a doctor blade coater with a gap of 230 μm. The slurry-coated foil is dried in an oven at 120 ° C. and then pressed using a calendar tool. Then, it is dried again in a vacuum oven to completely remove the residual solvent in the electrode film. Coin batteries are assembled in a glove box filled with argon. A separator (Celgard 2320) is placed between the positive electrode and the lithium foil used as the negative electrode. 1M LiPF ₆ in EC / DMC (1: 2) is used as an electrolyte and is dropped between the separator and the electrode. The coin battery is then completely sealed to prevent electrolyte leakage.

The coin battery test of the present invention, which is a conventional "constant cut-off voltage" test, follows the schedule shown in Table 1.

Each battery is cycled at 25 ° C. using a Toscat-3100 computer-controlled galvanostat cycling station (manufactured by Toyo). The coin battery test procedure uses a 1C current definition of 160mA / g. DQ1 (mAh / g) is the discharge capacity of the first cycle. The coin battery energy density can be calculated by the following equation.
Coin battery energy density (mWh / cm ³ ) = energy 1 (mWh / g) x PD (g / cm ³ )
Here, energy 1 is the integrated area of the capacitance-voltage plot in the first cycle, and PD is the press powder density measured in the above "A) Press Density Measurement (PDM)".

I) Full cell test

I1) Full cell preparation A pouch-shaped cell of 650 mAh or 1600 mAh is prepared as follows: positive electrode material, Super-P (Super-P, Timcal), graphite as a positive electrode conductive agent (KS-6, Maximal), and a positive electrode binder. Polyfluoride vinylidene (PVDF 1710, Kureha) as a dispersion medium so that the mass ratio of the positive electrode active material powder, the positive electrode conductive agent (super P and graphite), and the positive electrode binder is 92/3/1/4. To N-methyl-2-pyrrolidone (NMP) as. Then, the mixture is kneaded to prepare a positive electrode mixed slurry. Next, the obtained positive electrode mixed slurry is applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm. The typical filling weight of the positive electrode active material is about 11.5 ± 0.2 mg / cm ² for a 650 mAh battery and 14.0 ± 0.2 mg / cm ² for a 1600 mAh battery. The electrodes are then dried and calendared using a pressure of 120 kgf (1176.8 N). Further, an aluminum plate that acts as a positive electrode current collector tab is arc-welded to the end of the positive electrode.

A commercially available negative electrode is used. In short, a mixture of graphite, carboxy-methyl-cellulose-sodium (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 96/2/2 is applied to both sides of a 10 μm thick copper foil. A nickel plate that functions as a negative electrode current collector tab is arc-welded to the end of the negative electrode. The typical filling weight of the negative electrode active material is 8 ± 0.2 mg / cm ² . Lithium hexafluorophosphate (LiPF) at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 1: 1: 1. ₆ ) A non-aqueous electrolyte is obtained by dissolving the salt.

Separator made from a 20 μm thick microporous polymer film (Celgard® 2320, Celgard) inserted between the positive and negative electrodes to obtain a spirally wound electrode assembly. Sheet was spirally wound with a winding core rod. The assembly and electrolyte are then placed in an aluminum laminated pouch at a dew point of −50 ° C. in a drying chamber, thereby creating a flat pouch-type lithium secondary battery.

The non-aqueous electrolyte is impregnated at room temperature for 8 hours. The battery is precharged at 15% of its expected capacity and charged at room temperature for one day. Next, degas the battery and seal the aluminum pouch. Make the battery to be used as follows: reach the target voltage using 0.2C current in CC mode (constant current) and then reach the C / 20 cutoff current in CV mode (constant voltage). After charging the battery, the battery is discharged at a 0.5 C rate in CC mode to reduce the cutoff voltage.

I2) Cycle life test The prepared full-cell battery is charged and discharged several times at 25 ° C or 45 ° C under the following conditions, and the performance of the charge / discharge cycle is measured:
Charging is performed in CC mode at a rate of 1C until the target voltage is reached, and then in CV mode until C / 20 is reached.
The battery is then set to rest for 10 minutes.
Discharge to the cutoff voltage at 1C rate in CC mode.
The battery is then set to rest for 10 minutes.
The charge / discharge cycle is continued until the battery holding capacity reaches about 80%.
In all 100 cycles, discharge to the cutoff voltage is performed once at a rate of 0.2 C in CC mode.

If 80% retention capacity has not been reached by the end of the normal number of cycles, the expected number of cycles to obtain 80% retention capacity is calculated by a linear trend line.

I3) Full cell expansion test The battery prepared by the above preparation method is fully charged to the target voltage, inserted into an oven heated to 90 ° C., and maintained there for 4 hours. At 90 ° C., the charged positive electrode reacts with the electrolyte to produce gas, which causes the casing of the battery to expand. The increase in thickness ((thickness after storage-thickness before storage) / thickness before storage) is measured after 4 hours and is defined as the "full cell expansion" value.

The present invention will be further illustrated in the following examples.
Manufacturing Example 1
This example is used as Compound A in Examples to produce large polycrystalline lithium transition metal oxides with a very high Ni content, i.e. a Ni content of 80 mol% or more of the total transition metal content. The manufacturing process to be performed is shown. EX-A-01, EX-A-02, and CEX-A-01 have the same composition as Li (Ni _0.87 Mn _0.03 Co _0.10 ) O ₂ and are prepared by the following steps. To.
1) Precipitation of mixed transition metal hydroxides: MTH with narrow span PSD (MTH for EX-A-01 and EX-A-02) is continuously stirred tank reaction with manual backfeeding. Prepared using the instrument (CSTR) precipitation method. The temperature of the CSTR is fixed at 60 ° C. 2M MSO ₄ solution (M = Ni _0.87 Mn _0.03 Co _0.10 ), 10M NaOH solution, and 12M NH ₄ OH solution were added at 2 L / hour, 0.9 L / hour, and 0. It is continuously supplied to the 10 L reactor at a flow rate of 4 L / hour with a residence time of 3 hours. The CSTR is continuously stirred with an impeller of 1000 RPM. Precursor slurry is collected by overflow every hour. Precipitate the collected precursor slurry and discard the 2.8 L clear liquid portion. The remaining 0.5 L of concentrated slurry is manually returned to the CSTR every hour and supplied. During this procedure, the PSD of the precursor in the CSTR is measured. When the D50 particle size of the precursor first reaches 15 μm and then 20 μm, 5 L of precursor slurry is collected each time. The collected precursor slurry was filtered, washed with deionized water, and then dried at 150 ° C. for 20 hours in an _N2 atmosphere to MTH (Ni _{0.) of EX-A-01 and EX-A-02. 87} Mn _0.03 Co _0.10 O _0.19 (OH) _1.81 ) is obtained. CEX-A-01 MTH (Ni _0.87 Mn _0.03 Co _0.10 O _0.23 (OH) _1.77 ) is prepared by the same procedure as above, but with manual return supply. Prepared without normal span.
2) Blending: The prepared MTH is blended with LiOH as a lithium source at a target Li / M'molar ratio of 1.00 by a dry blending method.
3) Sintering: Each mixture of 300 g from step 2) is placed on an alumina tray and fired in an O ₂ atmosphere at 750 ° C. for 12 hours in a chamber furnace (direct sintering) to obtain a sintered product.
4) Post-treatment: The sintered product is ground and sieved to prevent the formation of aggregates and labeled EX-A-01, EX-A-02, and CEX-A-01.

Table 2 describes the PSD of the precursor, as well as the PSD, PD, and ID10 of compound A (increase in D10 after pressing). FIG. 1 shows an FE-SEM image of EX-A-01.

Manufacturing Example 2
This example is used as compound A in the examples to produce a large polycrystalline lithium transition metal oxide having a high Ni, i.e., a Ni content of 60-80 mol% of the transition metal content. show. The MTH of EX-A-03 (Ni _0.625 Mn _0.175 Co _0.20 O _0.29 (OH) _1.71 ) is MSO where M = Ni _0.625 Mn _0.175 Co _0.200 . ₄ Solutions are used and made by the process according to Production Example 1 except that the target D50 is 11 μm. EX-A-03 of formula Li _1.01 (Ni _0.625 Mn _0.175 Co _0.200 ) _0.99 O ₂ is double as described in WO 2017-042654. Obtained by sintering process. The process involves two separate sintering steps and is carried out as follows:
1) First Blend: To obtain a lithium-deficient sintered precursor, Li ₂ CO ₃ and MTH are uniformly blended with a Henschel mixer at a Li / M ratio of 0.85 for 30 minutes.
2) First sintering: The blend from the first blending step is sintered in an oxygen-containing atmosphere at 890 ° C. for 12 hours in a chamber furnace. After the first sintering, the sintered cake is ground, classified and sieved to prepare for the second blending step. The product obtained from this step is a lithium-deficient sinter precursor, i.e., the stoichiometric ratio of Li / M in LiMO ₂ is less than 1.
3) Second blend: In order to correct the stoichiometric amount of Li to Li / M = 1.02, the lithium-deficient sintered precursor is blended with LiOH · _H2O . Blend in a Henschel mixer for 30 minutes.
4) Second sintering: The blend from the second blend is sintered in an oxygen-containing atmosphere at 840 ° C. for 10 hours in a chamber furnace.
5) Post-treatment: The second sintered product is pulverized and sieved to prevent the formation of aggregates. The final product is a high Ni NMC polycrystalline Li _1.01 (Ni _0.625 Mn _0.175 Co _0.200 ) O ₂ , labeled EX-A-03.

CEX-A-02 is a commercially available product "CellCore HX12" manufactured by Umicore. Manufactured using a typical industrial CSTR precipitate and the MTH precursor prepared by the double sintering process described above. The composition is Li _1.01 (Ni _0.60 Mn _0.20 Co _0.20 ) _0.99 O ₂ . EX-A-04 is a fraction of the large particles separated from CEX-A-02 in the air separation process. NPK Corporation advances the air separation of CEX-A-02. 20% heavier particles are collected by air separation. The composition of EX-A-04 is Li _1.01 (Ni _0.625 Mn _0.175 Co _0.200 ) _0.99 O ₂ , which is slightly different from CEX-A-02 due to the design of MTH. different. Table 3 describes the PSD of the precursor, as well as the PSD, PD, ID10 (increased D10 after pressing), and IB (increased BET after pressing) of different compounds A.

From the data of EX-A-01 to 04 and CEX-A-01 and 02, it is clear that they have a very negative ID10 value and a very high IB value. A negative ID 10 means that the destruction of the particles reduces the D10 of the compound after pressing. Since the generated fine particles have a large surface area, the surface area after pressing should be large. The large surface area causes excessive side reactions during the cycle, which jeopardizes its use as a positive electrode material.

Manufacturing Example 3
This example shows a manufacturing process for producing a small lithium transition metal oxide used as compound B in the examples. High Ni NMC powder (EX-B-01, EX-B-) having the desired formula Li _1.01 (Ni _0.625 Mn _0.175 Co _0.200 ) _0.99 O ₂ and monolithic. 02, CEX-B-01, CEX-B-02) is obtained by a double sintering process. The process involves a lithium source, usually Li ₂ CO ₃ or LiOH, and a composition of Ni _0.625 Mn _0.175 Co _0.200 O _0.43 (OH) _1.57 , Korean Patent No. 101547972 (B1). ) Is a solid phase reaction with MTH prepared by the process described in No.. MTH has a D50 of about 4 μm. The process involves two separate sintering steps and is carried out as follows:
1) First Blend: To obtain a lithium-deficient sintered precursor, LiOH · _H2O and MTH are uniformly blended with a Henschel mixer at a Li / N'ratio of 0.90 for 30 minutes.
2) First sintering: The blend from the first blending step is sintered in a chamber furnace at 750 ° C. for 12 hours in an _O2 atmosphere. The product obtained from this step is a powdered lithium-deficient sinter precursor with Li / N'= 0.90.
3) Second blend: In order to correct the stoichiometric amount of Li (Li / N'= 1.02), the lithium-deficient sintered precursor is blended with LiOH · _H2O . Blend in a Henschel mixer for 30 minutes.
4) Second sintering: The blend from the second blend is sintered in an oxygen-containing atmosphere in a chamber furnace at various temperatures shown in Table 4 for 10 hours.
5) Post-treatment: The second sintered product is vigorously pulverized by a milling process to prevent the formation of aggregates. The final product is a high Ni NMC monolithic oxide with the formula Li _1.01 (Ni _0.625 Mn _0.175 Co _0.200 ) _0.99 O ₂ , EX-B-01, EX-B. Labeled as -02, CEX-B-01, and CEX-B-02.

CEX-B-03 is a commercially available Umicore product (CellCore ZX3) with an intermediate Ni content (less than 60 mol%), the composition of which is Li _1.03 (Ni _0.38 Mn _0.29 Co). _0.33 ) _0.97 O ₂ . This is obtained using the MTH produced by a typical CSTR precipitation process and the standard direct solid phase reaction between Li ₂ CO ₃ and MTH in an oxygen-containing atmosphere. CEX-B-04 is a commercial product (CellCore QX5) manufactured by Umicore having a very high Ni content, and its composition is Li _1.01 (Ni _0.80 Co _0.15 Al _0.05 ) ₀ . It is _.99 O ₂ . This is obtained using the MTH produced by a typical CSTR precipitation process and the standard direct solid phase reaction between LiOH · H ₂ O and MTH in an O ₂ atmosphere. Table 4 describes the morphology, PSD, PD, ID10 (increased D10 after pressing), and IB (increased BET after pressing) of the various compounds B. FIG. 2 shows an FE-SEM image of EX-B-02.

This table shows that as the temperature of the second sintering step rises, the final product becomes coarse, and in fact, at the temperature used for CEX-B-02, it is high enough to produce a very coarse monolithic product. Show that. The polycrystalline product has a very negative ID10 and a very high IB value.

Example 1
This example demonstrates the advantages of a bimodal composition comprising a large lithium transition metal oxide with a narrow span and a monolithic small lithium transition metal oxide. All products of Example 1 (Compound C) are obtained by a simple blending process using Compounds A and B described in Production Examples 1 and 3. Based on the fraction of B in Tables 5a-5d, compound A and compound B are weighed in a vial and the vial is shaken with a tubular mixer. The obtained compound C sample was analyzed by PD measurement and PSD measurement, and the results are shown in Tables 5a to 5d. The table also shows values for PD / 100 ^* (100 + ID10) (unit g / cm ³ ) and shows how the press density is affected by the brittleness of the particles.

FIG. 3 shows the PD (y-axis) and ID10 (x-axis) of the sample selection of Example 1. In the figure, only the sample with the highest PD is plotted among several different fractions of compound B in each mixture. CEX1 (Type 2) in Examples CEX1-14 has the highest PD, but its compressive strength derived from the ID10 value by the use of the large polycrystalline compound A with a wide span is as high as the compressive strength of EX1. It is not good, and as a result, the value of "PD x (100 + ID10) ÷ 100" becomes low. CEX1 (type 3) samples generally have lower PD and compressive strengths than EX1 samples. Comparing the data in Tables 5b and 5d with the data in Table 5c shows that the effect of using small polycrystalline particles of compound B is greater than that of using "normal" wide span compound A. From the data, it is possible to distinguish between mixtures according to the invention and those that are not part of the invention by setting the following restrictions: PD × (100 + ID10) ÷ 100> 3.20 g / cm. ³ , preferably ≧ 3.30 g / cm ³ .

Example 2
This example demonstrates the advantages of a bimodal mixture with a specific particle size and a small monolithic lithium transition metal oxide. All products of Example 2 (Compound C) are obtained by a simple blending process using Compounds A and B of Production Examples 1-3. Based on the fraction of B in Tables 6a-6e, compound A and compound B are weighed in a vial and the vial is shaken with a tubular mixer. The obtained sample of compound C was analyzed by PD and BET measurement, and the results are shown in Tables 6a to 6e.

FIG. 4 shows PD (y-axis) as a function of D50 (x-axis) of compound B. Among several different mixtures of Compound A and Compound B, the sample with the highest PD is plotted. The EX2 (type 1) sample is a mixture of a large polycrystalline compound having a D50 of 11 μm and a small monolithic compound B having a D50 of 2 to 4 μm. EX2 (type 2) is a mixture of a large polycrystalline compound having a D50 of 20 μm and a small monolithic compound B. Due to the use of larger polycrystalline compounds, the PD of EX2 (type 2) samples is high. When the D50 of compound B is higher than 4 μm in CEX2 (type 1), PD is reduced. Therefore, the D50 of compound B should be less than 4 μm. The CEX2 (type 2) sample is a mixture of large polycrystalline compound A and small polycrystalline compound B. The PD of CEX2 (type 2) is clearly dependent on the D50 of compound A, and for D50 = 11 μm (EX-A-03), the PD is not as high as the PD of EX2 (type 2). The effect of compound A (EX-A-04) with D50 = 20 μm is less clear. It is also clear that the IB of CEX2 (type 2) is higher than the IB of EX2 (types 1 and 2). Therefore, considering the effect of the increase in BET, the value of "PD x (100-IB) ÷ 100" representing the effect of the morphology of compound B is calculated, and the increase in BET adversely affects the cycle stability of the final product. Was considered to have. From the data, it is possible to distinguish between mixtures according to the invention and those that are not part of the invention by setting the following restrictions: PD × (100-IB) ÷ 100> 3.00 g. / Cm ³ , preferably ≧ 3.20 g / cm ³ .

FIG. 5 shows the increase in BET (IB, unit%, y-axis) after pressing as a function of the fractionation ratio (unit weight%, x-axis) of compound B. For CEX2-00, the amount of compound B is too small and the increase in BET is very important. The BET of the CEX2 (type 2) sample depends on D50 of compound A and increases significantly after pressing as a function of the ratio of compound B, "buffering" or "buffering" when compound B is a polycrystalline compound. Indicates that it has no effect. This is not the case for EX2 (Types 1 and 2) samples.

Example 3
Using samples of unmixed CEX-A-02 and EX-A-03, and mixed CEX2-07 and EX2-05, a positive electrode was prepared to measure the electrode density and to quantify the degree of electrode biting. do. The electrodes are labeled CEX3-01, CEX3-02, CEX3-03, and EX3, respectively. The relative electrode bite (REB) number (%) is obtained by the following equation.

The area is the area of the cross section of the Al foil cut perpendicular to the electrode surface.

Table 7 and FIG. 6 show the electrode densities (ED) and relative electrode bite (REB) of CEX3-01, CEX-02, CEX-03, and EX3.

R. E. B. The higher value means that the area of the Al foil in the electrode after the calendar processing is smaller than the area before the calendar processing. The cut area of the Al foil can be expected to be smaller as the Al foil undergoes compressive stress during the calendaring process. EX3, whose positive electrode material is EX2-05, has the lowest relative electrode bite and the highest electrode density. 7 and 8 show cross-sectional FE-SEM images of CEX3-02 and EX3 with the Al foil in the center. In EX3, the "buffering" effect of small monolithic particles is clearly visible.

Example 4
This example further demonstrates the advantages of bimodal mixtures with small monolithic compounds in terms of electrochemical properties when using surface treated compound C. This surface-treated product is prepared by the following steps.
1) First Blend: EX2-05 is blended with 0.2 wt% nanometer alumina powder in a Henschel mixer for 30 minutes.
2) First heat treatment: The blend from the first blending step is heated in a chamber furnace at 750 ° C. for 5 hours in an oxygen-containing atmosphere.
3) Second blend: The first surface-treated product is again mixed with 0.2% by weight nanometer alumina powder and 0.3% by weight of PVDF (polyvinylidene fluoride) powder for 30 minutes in a Henshell mixer. Blend with.
4) Second heat treatment: The blend from the second blending step is heated in a chamber furnace at 375 ° C. for 5 hours in an oxygen-containing atmosphere.
5) Post-treatment: The surface-treated product is sieved to prevent the formation of aggregates and labeled EX4.

A preferred source of Al is nanoscale alumina powder, such as fumed alumina. Alumina can be obtained by precipitation, spray drying, milling and the like. In one embodiment, the alumina typically consists of primary particles having a BET of at least 50 m ² / g and a D50 of less than 100 nm, which primary particles do not aggregate. In another embodiment, fumed alumina or surface treated fumed alumina is used. Fumed alumina nanoparticles are made in hot hydrogen air flames and are used in several applications for everyday products.

Typical examples of polymer PVDF powders are PVDF homopolymers or PVDF copolymers (such as HYLAR® or SOLEF® PVDF, both manufactured by Solvay SA, Belgium). Another known PVDF-based copolymer is, for example, PVDF-HFP (hexafluoropropylene). The particular PVDF grade used in this example is Arkema's Kynar Flex 2801-00, a PVDF copolymer resin.

The element Al is doped in the lithium metal oxide core by selecting the sintering temperature in the first heat treatment. Due to the lower sintering temperature in the second heat treatment, the crystal structure of alumina is maintained during the coating process and is found in the coating layer surrounding the lithium metal oxide core. Further, in the second sintering step, the Li-free fluorine-containing polymer starts to decompose when it comes into contact with the core material. When the polymer is completely decomposed, lithium fluoride is formed, which is found in the surface layer of the particles. LiF reacts with degradable polymers with lithium containing the surface bases of lithium transition metal oxides (composed of LiOH and Li ₂ CO ₃ as described in WO 2012/10731). Derived from. Although conventional fluoride-containing polymers melt quickly upon heating, it can be demonstrated that contact with Li (soluble) bases on the surface of transition metal oxides initiates chemical reactions that lead to the decomposition of the polymer.

CEX4-01 and CEX4-02 are EX4, except that EX-A-03 and CEX-A-02 (ie, compound A only) are used in the first blend instead of EX2-05, respectively. Prepared by the same procedure as. Table 8 shows the core material before surface treatment and the results of the full cell expansion test at 4.35 V.

The full-cell expansion in Table 8 indicates that EX4 coated with a mixture of polycrystalline NMC with narrow spans and a monolithic filler has less increase in thickness during the expansion test than CEX4-01 and CEX4-02. FIG. 9 shows the full cell cycle life of EX4, CEX4-01, and CEX4-02 on a 650 mAh pouch battery, 4.35 V-3.00 V (which is a relatively high voltage range for NMC compounds). EX4 has better cycle stability than CEX4-01 and CEX4-02.

Manufacturing Example 4
This example illustrates a manufacturing process for producing a large, spherical monolithic LCO used as compound A in the examples. EX-A-05 has a composition of Li (Co _0.979 Al _0.015 Mg _0.005 Ti _0.001 ) O ₂ and is prepared by the following steps.
1) Precipitation of Doped Cobalt Carbonate: Narrow span doped cobalt carbonate is prepared using a single batch stirrer reactor (STR) precipitation method. The temperature of the STR is set to 55 ° C. Cobalt chloride, 1.5 mol% aluminum sulphate, 0.5 mol% magnesium sulphate, and ammonium bisulfate are pumped simultaneously into the reactor to fill the STR with a mixture of these solutions. When the D50 particle size of the precursor reaches about 35 μm, the precursor slurry is collected. The collected precursor slurry is filtered, washed with deionized water and then dried to give the doped cobalt carbonate ((Co0.980Al0.015Mg0.005) CO3).
2) Roasting of doped cobalt carbonate: The doped cobalt carbonate is roasted at 600 ° C. for 8 hours in a roller kiln (RHK) to prepare a doped cobalt oxide.
3) First Blend: The prepared, doped cobalt oxide is blended with Li ₂ CO ₃ from a lithium source at a target Li / (Co + Al) molar ratio of 1.03 by a dry blend method.
4) First firing and post-treatment: The mixture from step 3) is placed on a mullite tray and fired in RHK at 1020 ° C. in a dry air atmosphere for 12 hours. The resulting first sintered cake is ground to give an intermediate product of lithium excess.
5) Second Blend: In order to correct the stoichiometric amount of Li to Li / (Co + Al) = 1.00, the intermediate product of lithium excess was added to 0.1 mol% of TiO ₂ and doped cobalt oxide. Blend with. Blend in a Henschel mixer for 30 minutes.
4) Second sintering: The blend from the second blend is sintered in an oxygen-containing atmosphere at 980 ° C. for 12 hours in a chamber furnace.
5) Post-treatment: The second sintered product is pulverized and sieved to prevent the formation of aggregates. The final product is a monolithic LCO Li (Co _0.979 Al _0.015 Mg _0.005 Ti _0.001 ) O ₂ labeled EX-A-05.

Table 9 shows the PSD of the precursor, and the PSD, PD, ID10 (increase of D10 after pressing) of EX-A-05, and the discharge capacity of the coin battery.

Example 5
This example demonstrates the advantages of a bimodal composition comprising a large monolithic LCO with a narrow span and a monolithic and small lithium transition metal oxide. All products of Example 5 (Compound C) are obtained by a simple blending process using Compounds A and B described in Production Examples 4 and 3. Based on the fraction of B in Table 10, compound A and compound B are weighed in a vial and the vial is shaken with a tubular mixer. Samples of the obtained compound C were analyzed by PD, PSD, coin cell and full cell measurements and the results are shown in Table 10. A 1600mAh pouch battery is used for the full cell test and the upper / lower limit of the cutoff voltage is 4.45V / 3.00V. CEX5-03 is Umicore's CellCore XD20, which is a commercially available current doped bimodal LCO product prepared according to Example 1 of WO 2012/171780.

EX-A-05, a large, monolithic, doped LCO compound A, has a relatively higher press density and lower DQ1 than the NMC compound due to the unique properties of the monolithic LCO compound. Press density can be further improved by mixing small monolithic NMC compounds with an optimum fraction of 20%. Due to the larger capacity of the monolithic NMC, the EX5 has a larger capacity than the EX-A-05. Higher PD and higher DQ1 result in higher volumetric energy density of EX5.

Battery blistering at high voltages such as 4.45V is one of the biggest problems in high voltage applications. For example, the thickness of a full-cell pouch battery manufactured by CEX5-03 is increased by 300% after the expansion test. The increase in thickness of the full-cell pouch battery manufactured by EX5 is much smaller than that of CEX5-03. A full cell test was performed. FIG. 10 shows the relative capacity as a function of the number of cycles in a full cell. It is clear that EX5 has better cycle stability than CEX5-03.

Claims (9)

A bimodal lithium transition metal oxide powder mixture for rechargeable batteries.
The particles of the material A having a layered crystal structure composed of the element Li, the transition metal composition M, and oxygen are contained, and the particles of the material A are of the general formula Li _{1 + a} Co _{1-m M'm} O ₂ [in the formula,-. 0.05 ≦ a ≦ 0.05 and 0 ≦ m ≦ 0.05, where M'is a metal group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, and V. A first lithium transition metal oxide powder having a particle size distribution in which the first powder has a span of less than 1.0. Lithium transition metal oxide powder and
It has a monolithic form, and the general formula Li _{1 + b} N'1 _-b O ₂ [in the formula, -0.03 ≤ _b ≤ 0.10, and N'= Ni _x M " _y Coz _Ed , 0. .30 ≦ x ≦ 0.92, 0.05 ≦ y ≦ 0.40, 0.05 ≦ z ≦ 0.40, and 0 ≦ d ≦ 0.10. M ”is one of Mn or Al. A second lithium transition metal oxide-based powder comprising a material B having [E is a dopant different from M', which is either or both," said the first powder is 10-. The second powder has an average particle size D50 of 40 μm, the second powder has an average particle size D50 of 2-4 μm, and the weight ratio of the second powder in the bimodal mixture is 15-60 weight. %, A bimodal lithium transition metal oxide powder mixture. The bimodal powder mixture according to claim 1 , wherein the material A has a D50 of 20 μm or more, and the weight ratio of the second powder in the bimodal mixture is 15 to 25% by weight. Claim 1 in which E is any one or more of the elements in the group consisting of Al, Ca, Si, Ga, B, Ti, Mg, W, Zr, Cr, V, S, F, or N. The described bimodal powder mixture. The bimodal powder mixture according to claim 1, wherein the first powder has an average particle size D50 of 10 to 25 μm and a span of 0.8 or less. The bimodal powder mixture according to claim 1, wherein both the first powder and the second powder have an aspect ratio of around 1. The bimodal powder has a first corrected press density of 3.2 g / cm ³ or more, and the first corrected press density is calculated by the formula PD / 100x (100 + ID10) in the formula. , PD is the press density under a pressure of 200 MPa, and ID10 is the increase in the D10 value in the particle size distribution of the bimodal powder calculated as follows.

The bimodal powder mixture according to claim 1, wherein (D10 after PDM) and (D10 before PDM) are D10 values after and before application of a pressure of 200 MPa, respectively. The bimodal powder has a second corrected press density of 3.0 g / cm ³ or greater, and the second corrected press density is calculated by the formula PD / 100x (100-IB). In the formula, PD is the press density under a pressure of 200 MPa, and IB is the increase in the specific surface area BET of the bimodal powder calculated as follows.

The bimodal powder mixture according to claim 1, wherein (BET after PDM) and (BET before PDM) are BET values after and before application of a pressure of 200 MPa, respectively. The bimodal powder mixture according to claim 1, wherein the particles of the powder mixture have a surface layer containing a homogeneous mixture of elements of LiF and Al ₂ O ₃ . A positive electrode mixture for a rechargeable battery, comprising the bimodal powder mixture according to claim 1, a binder, and a conductive agent, and the weight ratio of the bimodal powder mixture in the positive electrode mixture is determined. A positive mixture for rechargeable batteries, which is at least 90% by weight and the positive mixture has a density of at least 3.65 g / cm ³ when pressed under 1765.2 N.

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